If you apply for a job at a bank, you wouldn't hide your experience in programming microcontrollers or logistics solutions, so why hide a mobile game from a mobile company?

Just make sure you don't derogate your accomplishments by eccessively calling it "hobby project", if you do it with your professional skillset, it's as much a valid project as most employeers projects.

That doesn't mean you should lie about that, just don't focus on the "hobbyness", focus on the project's merits.

Only if they ask you about your hobby projects. Don't shoe horn it in - I'd find that weird
Don't just bring it up with no relevant prompting, if you speak for fifteen mins abotu a project no one has asked you about it won't look good. The employer will have questions they want to ask fit around them not the other way around.

Most interviews i experienced started with a general "please tell us something about yourself", which seemed to be made to include acomplishments. In this context, i wouldnt find it "shoehorning" to talk about hobby projects, if one considers them an accomplishment
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kepplaMay 31 '12 at 13:38